Several optical noncontacting detecting means have been proposed as follows:
(1) Traditional means to introduce the motion of the real image of a light spot in the direction of optical axis or that perpendicular thereto through a slit or a screen to a photocell.
(2) Means providing a vibrating pinhole where the real image of a light spot is formed so that the image displacement in the direction in which the pinhole vibrates be determined from the difference in phase between the vibration of the pinhole and the variation in the intensity of the light passing therethrough (known as the pinhole vibration method).
(3) Means giving an oblique observation relative to the axis of light projection so that the displacement of a light spot in the direction of the light projection axis on the surface being detected be converted as the lateral motion of the image, from which differential output is obtained through two photocells provided directly over the plane where the image is formed.
(4) Means directly measuring the displacement in the surface being detected by trigonometry based on a reference length established within the detector (such as the detector utilizing phase difference between incident and reflected wave, and the detector with rotary mirror).
However, these conventional detecting means have encountered several problems, such as a low signal/noise (S/N) ratio with weak signal input, a complex lay out of optical system, and an increase in apparatus size and weight. Particularly, the means (4) cannot utilize a change in the intensity of the light as the varying quantity for detection, because the intensity of input signal light is strongly affected by the direction of the normal at the surface of the object being detected. Therefore, it is difficult to provide a versatility such as a function to detect normal directions of the surface of the object simultaneously or independently.
The object of this invention is to solve these problems with the conventional detecting means by providing an optical noncontacting detector that comes with a high S/N ratio, simple optical system, small size, light weight, solidly built and applicability to wide use.